Re: A proposal for Debian policy for Ada

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Sun, 16 May 2010 22:48:19 +0200, Ludovic Brenta wrote:

> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>> In the past we are used to link external libraries using package Linker and
>> Default_Switches ("ada") set to, e.g. "-lgdk_pixbuf-2.0". The problem with
>> this approach is that Linker package is not automatically inherited. There
>> exist different workarounds all more or less unpleasant.
>>
>> Meanwhile there is IMO a cleaner and simpler way. Just create a gpr file
>> for the library(es) in use. For example:
>>
>> project Gdk_Pixbuf is
>>    for Externally_Built use "true";
>>    for Source_Files use ();
>>    for Library_Dir use "/usr/lib"; -- Where it resides
>>    for Library_Name use "gdk_pixbuf-2.0"; -- Its name (no ".so" ending)
>>    for Library_Kind use "dynamic"; -- Shared in this case
>> end Gdk_Pixbuf;
>>
>> Then with it in your project:
>>
>> with "gdk_pixbuf.gpr";
>> project My_Library is
>>    ... -- No linker package needed
>> end My_Library;
>>
>> That is. gnatmake and gprbuild will add necessary linker options to all
>> projects referencing My_Library.
>>
>> What about adding this as a requirement to the Debian policy?
> 
> It seems you forgot to read �5.3.6 GNAT project file and �6 Using shared
> libraries.

5.3.6 seems to refer to the Ada library being packaged. What I mean is a
way to reference to an external C library, e.g. libgdk_pixbuf in the
example.

As for 6, it gives an example

with "LIBRARY";
project PROGRAM is
   for Source_Dirs use (".");
   for Object_Dir use "obj";
   for Exec_Dir use ".";
   for Main use ("PROGRAM");
   package Linker is
      for Default_Switches ("Ada") use ("/usr/lib/libLIBRARY.a");
   end Linker;
end;

that uses Default_Switches. It were not necessary if the LIBRARY.gpr (in
5.3.6) described both static and dynamic builds controlled by Library_Type
variable. gnatmake is smart enough to choose either *.a or *.so for the
dependant library/application. E.g.

project LIBRARY is
   type Library_Kind_Type is ("static", "relocatable");
   Library_Kind : Library_Kind_Type :=
      external ("Library_Type", "relocatable");
   for Library_Kind use Library_Kind;
   for Library_Name use "LIBRARY"; -- Valid for either choice
   for Library_Dir use "/usr/lib"; -- Valid for either choice
   ...
   for Externally_Built use "true";
end LIBRARY;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de